1. Field of the Invention
The present invention relates generally to an exhaust gas recirculation system for an internal combustion engine of a vehicle which system is provided with an altitude correction device.
2. Description of the Prior Art
As is well known in the art, an internal combustion engine is provided with an exhaust gas recirculation (EGR) system for recirculating exhaust gases of the engine into air taken thereinto to reduce the amount of nitrogen oxides (NOx) produced by combustion in the engine.
Since the exhaust gases fed into the engine taken air are considered to be inert gas which serves to limit combustion temperature in the engine, when a proper quantity of exhaust gases are recirculated, the recirculated exhaust gases are extremely effective for reduction in the production of nitrogen oxides. However, when an excessive quantity of exhaust gases are recirculated, the recirculated exhaust gases exert a bad influence on the combustion in the engine or the stability of operation of the engine.
As an example of the cases in which the recirculated exhaust gases have a bad influence on the operation of an engine, the case is considered in which the engine is running on a land having a high altitude.
Since as the altitude is increased, the atmospheric pressure is reduced to reduce the density of air, the amount of oxygen fed into the engine is reduced to cause change or decrease in the air-fuel ratio set for the operation of the engine on a land having a low altitude. Thus, as is well known in the art, the fuel supply system of an engine is provided with an altitude correction device for reducing the amount of fuel fed into the engine to a proper value in accordance with increase in the altitude to correct the air-fuel ratio of the engine to a predetermined desired value.
However, a conventional EGR control system has not been provided with an altitude connection device for reducing the amount of exhaust gases recirculated into the engine taken air when the altitude is increased. As a result, the conventional EGR control system has undergone inconveniences that an EGR ratio of the flow of recirculated exhaust gases to the flow of engine taken air is excessively increased to exert on the stability of operation of the engine a bad influence such as, for example, stopping the operation of the engine when the engine is running on a land having a high altitude.